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I have a spare set of stock XS 650 carbs you can have. I am pretty sure the diaphragms are still good in them. I'll have to dig them out of my carburetor tub and take a look. They are yours if you want them.
Interesting. Last sets of XS carbs I had here for spring cleaning I was sure had the same diaphragms as all the BS40 sets I have done, but I didn't measure them to be sure they were exactly the same. The slides may be different diameters. I'd have to check my notes and dimensions.
I'm sure that with your attention to detail and meticulous work, that you would/did check those dimensions to be sure.